Monday, 21 January 2013

In Response to some questions relating to the effort vs reliability of players of this age

I've not had a CDM4 fail on me yet. This is the 7th or 8th player with that mech that I've had including the CD850MKII I had from new which I finally sold about 4 years ago. They do all suffer with the loading gear issue and also a failed cap on some of the earlier machines (a blue 33uF Philips axial jobbie) that causes read and tracking issues. The cap is a different make on this model but I will get to it later when I recap the rest of the player. 

With respect to the opamps, I've changed opamps on many players now and by the time the PSU including local decoupling caps have been changed and the filter treated to some better components, I've yet to hear an adverse reaction to these HA's that I've got fitted. The LME47920 is one of the best opamps for audio in my opinion but as I have stated, I've fitted gold rolled pin sockets to allow for opamp rolling and I've got a few options that I'll try when I've finished the rest. I do appreciate that if the filter is poorly designed then there is potential for issue. The HA's are expensive and may not ultimately fit the budget and depending on other work in the whole output stage my be a little OTT 

I'm trying to keep the thread as informative as possible just in case someone else fancies tackling something similar. The principles are the same for pretty much everything. Its all about the PSU, reducing noise and separating PSU rails to keep the noise from one part of the player effecting everything that shares that rail. As an example, there are several things on the +5v rail including the CPU, DAC analogue, DAC digital, digital filter and SPDIF driver to name but a few. Digital rails are especially noisy. Even fitting separate basic regulators (7805 @ 22p each) to each individual device supply pin in place of the original shared for everything will stop noise from one device being transferred around the original 5v rail. I describe this as separating the noise domain. In many players each device is fed via a supply resistor which can be removed making it easy to fit independent regs. There are some chip type regulators available now with very good noise figures which are very cheap. These are what I will use in this player. I have my own discrete low noise regs but I'm looking to complete as cheaply as possible and I'm very confident I can achieve a very high level of performance using good quality LDO low noise chip type regs.

I'll post the details of each section I change and show how I work out that cap does what job (analogue/Digital) and what I change it to along with my opinion on why. I'm now waiting for supplies before I move on but I'll show some of my working's out over the next few evenings :-)

PSU Diagram

Here's the PSU updates on the circuit diagram